[ANSWERED] Oil life monitor calibration same for dry and wet sump?
11-15-2018, 03:25 PM
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[ANSWERED] Oil life monitor calibration same for dry and wet sump?
The original question is here.
Patman asked:
I'm curious if the algorithm is exactly the same for the oil life monitor on the dry sump equipped cars as it is for the wet sump equipped cars? With the extra 3 quarts of oil in the dry sump (30% more oil), in theory the oil should last longer between changes and therefore I wonder if the OLM allows for that extra mileage possibility? Also, how does the OLM take into account both the time factor and the mileage factor?
I'm curious if the algorithm is exactly the same for the oil life monitor on the dry sump equipped cars as it is for the wet sump equipped cars? With the extra 3 quarts of oil in the dry sump (30% more oil), in theory the oil should last longer between changes and therefore I wonder if the OLM allows for that extra mileage possibility? Also, how does the OLM take into account both the time factor and the mileage factor?
Tadge answered:
Great question, Patman. This is one I bet a lot of people are curious about. Obviously, maintaining the quantity and quality of the oil in your engine is paramount for long term durability and performance. There are many things that work to deteriorate the quality of your oil and we make the oil life monitor (OLM) as accurate as we can to predict oil life in consideration of all of those variables. The simplest variable is the length of time the oil is in the engine. As you surmise in your question, this is an important variable. Oil ages sitting inside your engine differently than in a sealed container. It is exposed to more oxygen, humidity, various sealants and a variety of metals in your engine. Also, time causes things you might not expect to have an influence such as oxidation of your oil filter. To account for this variable there is an OLM clock that begins a year-long count down every time it is reset. So that is the best you can do…. Change your oil and filter once a year.
You also surmise that mileage should be a factor. We could use mileage, but it is more accurate to actually count combustion events. Every time the fuel and oxygen ignite in the cylinder a tiny quantity of contaminants slip past the piston rings and gets into your oil. Over time, these contaminants build up and hurt the oil’s lubrication capability. You can see this effect as the oil darkens over time.
OK, but all combustion events are not created equal, right? There is a big difference between cruising down the highway under light load and tearing it up on the track. On the highway, the coolant and oil stay relatively cool and there is little stress on the engine. On the track, when oil temps are high, oil molecules actually fracture and that hurts lubrication performance. We handle that buy adding a multiplier that compounds the number of combustion events that occur at higher temperatures. The hotter the oil, the more heavily we weight those events and the shorter the life prediction. On the other hand, running your engine at low temperatures stresses the oil as well. So we also have a multiplier that over-weights combustion events when it is cold. People who drive in cold climates and take relatively short trips are going to find they have shorter oil life. The display in the cluster is regularly updated to the lesser of the time-based or use-based metrics.
Lastly, to get to the first part of your question: No, the dry-sump cars do not use the same algorithm as the wet-sump. As you theorize, having more oil dilutes contamination and distributes thermal stress across a greater quantity of oil. Those are both true and, even though you get some life extension, it is not in direct proportion to the total quantity of oil in the system. Why not? Well the time-based degradation is very insensitive to oil quantity. And don’t forget the oil in dry-sump cars get more exposure to air and system metals (and other materials) because of the tank and plumbing. The extra oil quantity helps roughly in proportion to volume for contamination, but not quite in proportion when it comes to thermal stress. Since dry-sump cars are more likely to see track duty or hard street driving we tend to be a little conservative to make sure oil is changed before it falls below a performance level needed to assure perfect operation of your engine. Bottom line is that, depending how you use your car, the dry sump will have at least the life of wet sump, and probably somewhat more.
Great question, Patman. This is one I bet a lot of people are curious about. Obviously, maintaining the quantity and quality of the oil in your engine is paramount for long term durability and performance. There are many things that work to deteriorate the quality of your oil and we make the oil life monitor (OLM) as accurate as we can to predict oil life in consideration of all of those variables. The simplest variable is the length of time the oil is in the engine. As you surmise in your question, this is an important variable. Oil ages sitting inside your engine differently than in a sealed container. It is exposed to more oxygen, humidity, various sealants and a variety of metals in your engine. Also, time causes things you might not expect to have an influence such as oxidation of your oil filter. To account for this variable there is an OLM clock that begins a year-long count down every time it is reset. So that is the best you can do…. Change your oil and filter once a year.
You also surmise that mileage should be a factor. We could use mileage, but it is more accurate to actually count combustion events. Every time the fuel and oxygen ignite in the cylinder a tiny quantity of contaminants slip past the piston rings and gets into your oil. Over time, these contaminants build up and hurt the oil’s lubrication capability. You can see this effect as the oil darkens over time.
OK, but all combustion events are not created equal, right? There is a big difference between cruising down the highway under light load and tearing it up on the track. On the highway, the coolant and oil stay relatively cool and there is little stress on the engine. On the track, when oil temps are high, oil molecules actually fracture and that hurts lubrication performance. We handle that buy adding a multiplier that compounds the number of combustion events that occur at higher temperatures. The hotter the oil, the more heavily we weight those events and the shorter the life prediction. On the other hand, running your engine at low temperatures stresses the oil as well. So we also have a multiplier that over-weights combustion events when it is cold. People who drive in cold climates and take relatively short trips are going to find they have shorter oil life. The display in the cluster is regularly updated to the lesser of the time-based or use-based metrics.
Lastly, to get to the first part of your question: No, the dry-sump cars do not use the same algorithm as the wet-sump. As you theorize, having more oil dilutes contamination and distributes thermal stress across a greater quantity of oil. Those are both true and, even though you get some life extension, it is not in direct proportion to the total quantity of oil in the system. Why not? Well the time-based degradation is very insensitive to oil quantity. And don’t forget the oil in dry-sump cars get more exposure to air and system metals (and other materials) because of the tank and plumbing. The extra oil quantity helps roughly in proportion to volume for contamination, but not quite in proportion when it comes to thermal stress. Since dry-sump cars are more likely to see track duty or hard street driving we tend to be a little conservative to make sure oil is changed before it falls below a performance level needed to assure perfect operation of your engine. Bottom line is that, depending how you use your car, the dry sump will have at least the life of wet sump, and probably somewhat more.
Last edited by jvp; 11-15-2018 at 03:26 PM.
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11-16-2018, 08:25 AM
#2
Very interesting and exhaustive answer from Tadge, as usual! Highly appreciated!
I will have been interested to also know on why ensuring that your oil level is good, differs that much between models? On some do it on a cold engine, on others, once oil is at temp, wait for 5 to 10minutes max, and perform the check, etc... this ends to sometimes users confusion and or mistake that can potentially conducts to a disaster.
It will be so great to have one single way to check it (best on cold engine before your start in the morning), or even an oil gauge as on some Porsche.
Just my 2 cent
Phil
I will have been interested to also know on why ensuring that your oil level is good, differs that much between models? On some do it on a cold engine, on others, once oil is at temp, wait for 5 to 10minutes max, and perform the check, etc... this ends to sometimes users confusion and or mistake that can potentially conducts to a disaster.
It will be so great to have one single way to check it (best on cold engine before your start in the morning), or even an oil gauge as on some Porsche.
Just my 2 cent
Phil
11-16-2018, 10:52 AM
#3
Instructor
#2 Phil - While dry sumps can be a slight pain to check oil since they are different from process used for years on wet sump engines - I first ran across dry sump protocol 18 years with motorcycles with dry sump. I typically check wet sump engines prior to starting in the morning except on our 2018 Fusion Sport which states warm engine to operating temperature, shut off engine, & wait 15 minutes. Only wet sump vehicle that I have seen this protocol on.
#1 - Tadge response on oil life monitor - Very good with well explained detail. Due to low annual mileage & street driving, our 2016 with dry sump will always fall under the 1 year time limit.
#1 - Tadge response on oil life monitor - Very good with well explained detail. Due to low annual mileage & street driving, our 2016 with dry sump will always fall under the 1 year time limit.
Last edited by JHundertmark; 11-16-2018 at 10:53 AM.
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11-16-2018, 05:49 PM
#4
Of course most BMW wet sump engines now don't have dipsticks so you can't check the oil when the car hasn't been fired up anyway.
11-17-2018, 12:00 PM
#5
Melting Slicks
I don't know about the C7 but the OLM on my '13 GS with dry sump does not count down from one year. It's been about 15 months since I last changed it and it is on 37% not zero.
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11-17-2018, 05:15 PM
#6
Race Director
If I'm not mistaken, the "one-year since reset" OLM countdown was introduced with the C7 (LT1 engine for 2014 m-y).
Last edited by Gary '09 C6; 11-17-2018 at 05:15 PM. Reason: sp
11-17-2018, 10:21 PM
#7
The stock answer of; "change your oil once year," doesn't address at all the olm that doesn't have the ability to determine oil quality. That's out of it's parametric agility. The original oil fill in my bought new C7, is going on 2.5 years old, and still has yet to time out. That means that the olm is nothing more than a timer, if you will. Since it certainly cannot ascertain the actual age OR quality of the crankcase oil. It signifies that the olm, isn't actually capable of measuring anything meaningful as pertains to whether the oil needs replacing or not. The people who are assuming that their low mileage or no mileage oil is bad on Day 366 of the oil fill, seemingly aren't aware of the olm's inability to provide a scientific chemical analysis of the oil's quality to them.
Last edited by Skid Row Joe; 11-17-2018 at 10:27 PM.
11-21-2018, 07:26 AM
#10
Melting Slicks
The stock answer of; "change your oil once year," doesn't address at all the olm that doesn't have the ability to determine oil quality. That's out of it's parametric agility. The original oil fill in my bought new C7, is going on 2.5 years old, and still has yet to time out. That means that the olm is nothing more than a timer, if you will. Since it certainly cannot ascertain the actual age OR quality of the crankcase oil. It signifies that the olm, isn't actually capable of measuring anything meaningful as pertains to whether the oil needs replacing or not. The people who are assuming that their low mileage or no mileage oil is bad on Day 366 of the oil fill, seemingly aren't aware of the olm's inability to provide a scientific chemical analysis of the oil's quality to them.
Tadge - Thanks for the information, and most of us really enjoy your feedback on important issues.
Last edited by LIStingray; 11-21-2018 at 07:27 AM.
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12-03-2018, 06:44 AM
#11
12-03-2018, 06:50 AM
#12
The stock answer of; "change your oil once year," doesn't address at all the olm that doesn't have the ability to determine oil quality. That's out of it's parametric agility. The original oil fill in my bought new C7, is going on 2.5 years old, and still has yet to time out. That means that the olm is nothing more than a timer, if you will. Since it certainly cannot ascertain the actual age OR quality of the crankcase oil. It signifies that the olm, isn't actually capable of measuring anything meaningful as pertains to whether the oil needs replacing or not. The people who are assuming that their low mileage or no mileage oil is bad on Day 366 of the oil fill, seemingly aren't aware of the olm's inability to provide a scientific chemical analysis of the oil's quality to them.
Last edited by Kozzzz; 12-03-2018 at 06:51 AM.
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12-15-2018, 08:23 PM
#14
Seems as if many owners are always looking for ways to use another oil than what GM recommends for whatever their reasons. Got me thinking, just maybe the OLM algorithms must be tied specifically to the use of Mobil 1 Dexos2 oil GM recommends. This would suggest using the OLM for any other oil more than likely would be inaccurate for these people.